Mountains are looking awesome now! Thanks for the alt textures!
I'd like to see Helgen done. Purely because it's the first place you see and to me it sets the bar for what the other towns will look like.
I'd second this, particularly the forts (which ties in with the architecture requests nicely). When I first started playing the game and had to run into that tower after getting off the execution block, I was genuinely horrified by the muddy wall textures inside. Such a stark contrast to the character detail that it hurt my face.